Medication treatment for opioid use disorder (OUD) remains an underutilized evidence-based practice. Washington State used federal Opioid-STR funding to develop and implement the Washington State Hub and Spoke Model (H&S), an integrated care model to expand access to OUD medications (buprenorphine, methadone, naltrexone). Their model is a flexible approach incorporating primary care and substance use treatment programs, referral organizations, nurse care managers and care navigators. Based on the initial success in an original 6 H&S networks and aiming to increase access in underserved and marginalized populations, Washington funded 5 more H&S networks and developed a second-generation, low-barrier H&S model, to place medication initiation sites in 17 non-traditional settings such as emergency departments, syringe exchanges, jails, and homeless shelters, with connections to community partners who will offer OUD medication maintenance. The proposed study expands the research team?s activities funded under RFA DA- 18-005 by studying implementation and effectiveness of the new H&S model. We maintain a hybrid effectiveness-implementation approach, and utilize social network analysis to understand how and how well H&S networks develop to serve the OUD population. Thus, the specific aims for the proposed study are: 1) Examine the implementation and effectiveness of the expanded first- and second-generation H&S models in addressing OUD (e.g., initiation of and retention in OUD medication treatment, overdose, employment, criminal justice involvement), extending our original NIDA study. 2) Conduct a social network analysis among all H&S networks that will describe patterns of connection, coordination, and integration among organizations; how the two types of H&S networks build upon each other and how they differ; and what pathways of OUD medication treatment clients use within and across networks. 3) Test the relationships between network features identified in Aim 2 (e.g. network characteristics and treatment pathways) and effectiveness of the first- and second- generation H&S models. The study will focus on adults (18+) with OUDs in Washington who are enrolled in Medicaid, about 90% of people with OUDs in treatment in Washington. Statistical methods will be used to ensure a rigorous quasi-experimental design. The findings will enable us to understand what makes the H&S model effective for increasing OUD medication treatment and improving outcomes for people with OUD, for whom, and how to expand the reach to individuals who may not seek treatment. Wide dissemination efforts in the form of issue briefs and guidelines will support states and providers to implement flexible H&S models that incorporate nurse care managers, care navigators, and low-barrier OUD medication initiation. Thus, we will be able to help ensure ?no wrong door? to enter treatment and access to the treatment models with the best success for promoting recovery.